Virtual Ground Concept

VGfeature

Virtual Ground Concept:

Virtual Ground Concept, As the name suggests Virtual Ground is making a node or a connection virtually ground. By the term virtually ground I mean, its not physically connected to Ground but voltage at that point/node is ‘0V’ so we refer to it as Ground. This concept is used for Analysis of Operational Amplifier Circuits. It makes analysis of OP-Amp based circuits very easy.

What happens in Virtual Ground:

Virtual Ground Concept

Virtual Ground Concept

Consider an Inverting Op-amp Configuration with negative feedback. Referring to Ideal Op-Amp parameters, Input Impedance is ∞. So ideally no current flows through Op-amp.

As there is no current flowing through Op-amp, Current (Ia) flowing through node Va will be ‘0’. And by Ohm’s Law we could conclude that Va=0. V= I X R, as I is 0 perhaps V will also be ‘0’.

Another Example to Understand Virtual Ground Concept:

For Ideal Op-Amp Configuration, differential input voltage is ‘0’, ie.

V(non-inv) — Vinv =0
So ideally Vinv = Vnon-inv.

In Inverting Configuration, Vnon-inv is connected to ground. And as Vinv = Vnon-inv, Vnon-inv=0 so Vinv is also equal to ‘0’. Ground is nothing but a point with voltage ‘0’ as voltage at  these terminals is zero we can refer them as ‘Virtual Ground’.

They aren’t physically connected to Ground but as they posses zero voltage they are termed as Ground.

Note: Virtual Ground Concept is applied only during analysis of Negative Feedback,Inverting Configuration of Op-Amp

Virtual Short Concept:

Further, we could also derive Virtual Short Concept from above example. As discussed earlier:

For Ideal Op-Amp Configuration, differential input voltage is ‘0’, ie.

V(non-inv) — Vinv =0
So ideally Vinv = Vnon-inv.

This implies that voltages at both the pins are equal ideally, so this suggests that both pins are Virtually Short with each other.

Virtually Short as there no physical shorting between both the pins, they are considered to be shorted for better analysis of Complex Op-amp based circuits.

PS:Virtual Short Concept is applied only during analysis of Negative Feedback,Inverting Configuration of Op-Amp

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